<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        function foo(){
            console.log(this.a)
        }

        var p1 = {
            a:4,
        }

        var p2 = {
            a:5
        }

        var bar = foo.bind(p1);

        bar();                  // 4
        bar.call(p2)            // 4

        var baz = bar.bind(p2)
        baz();                  // 4
        // 说明一旦经过显式绑定之后就不能更改了,无论调用bind,apply,call都无法更改，只有new绑定可以更改


    </script>
</body>
</html>